At high-speed processing, high kinetic energy is used to form and/or process a material body. In connection with high-speed processing, striking machines are used where the press piston has essentially higher kinetic energy than at conventional processing. The press piston often has a speed, which is about 100 times higher or more than in conventional presses in order to perform cross-cutting and punching, forming of metal components, powder compacting- and similar operations. In high-speed processing there is a number of different principles to achieve the high kinetic energies necessary for the achievement of the advantages which the technique offers. A great number of different machines and methods accelerating a striking body has been developed, e.g. as shown in WO 9700751. Common for all these machines, whether they for the acceleration use air, oil, springs, air-fuel mixtures, blasting agents or electro-mechanics, has been that one has in principle triggered an uncontrolled process which results in the striking body accelerating towards a tool, and that one has thereafter in some way moved the striking body back after a certain time. Further, the accelerating forces have continued to effect the striking body after the first stroke, which has resulted in that several strokes have occurred after the first stroke. These additional strokes, re-strokes, are undesirable and often directly detrimental. Also in the case when a forming tool is used, e.g. at the forming of patterned plates, it is of vital importance that the forming tool does not come into contact with the blank two times or more as there then is a risk that the tolerances of the plates is not met.
Thus, it has been identified that principally without exceptions it is a drawback to subject the work-piece to be processed in a high speed process to more than one stroke. This applies whether it is the question of cross-cutting, homogeneous forming or powder compacting. When it the question of cross-cutting, the additional unnecessary strokes may result in excessive tool wear and undesired burrs. At punching, smearing, welding, burrs and tool wear may occur. At homogeneous forming, there is the risk that undesired material changes occur, punches may crack, and the blank may be clamped unnecessarily hard in the matrix, which results in the forming force increasing with matrix wear as a consequence. At powder compacting with brittle materials such as ceramics, hard metals and the like, a second stroke may wreck the continuous body which one has managed to create in the first stroke. At powder compacting of soft powders such as copper and iron, for instance, the density will indeed continue to increase, if one strikes several times, but the blank is clamped even harder in the matrix with an increased number of strokes, which results in undesirable wear. A feasible reason for the fact that focus has not previously been put on this problem might be that these progresses are very rapid and may in many cases not been able to be observed, and therefore the detrimental effects of the re-stroke have seemed to be unexplainable. Further, the enormously short reply terms, which are required to make it possible to interrupt the acceleration of the striking body after the first stroke, imply a complication as such. If one accelerates a striking body by means of some gas, it has in principle been technically impossible to reduce the pressure in the drive chamber during the short time between the first and the second stroke (typically between two and fifty milliseconds). By means of hydraulics, it is technically possible, but most of the valves on the market have too long an adjustment time to be able to be used at the short adjustment times which may be required, often an adjustment within twenty milliseconds. As to spring machines, it is rather evident that it is somewhat difficult to form a mechanical device slacking on the spring bias within a few milliseconds. As indicated above, most known hydraulic high speed machines are equipped with valve mechanisms which cannot be adjusted quick enough to hinder the advancing oil and hence the creation of pressure in the drive chamber of the piston. The reason for this is that hydraulic valves for high flows (300 to 1000 litres/minute) normally require comparatively long adjustment times. This depends in its turn on the fact that the valve body quite simply has to move a comparatively long distance so that an enough large opening area will be created so that the oil will be able to pass through it without too large a pressure fall.